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Air Brakes on Steam Locomotives
With the coming of steam to Run8 (with the GS-4's promised on the Run8 Studios site) I thought it would be good to review how the engineer worked the brakes on steam, and how it differs from equipment in current use. Knowing that there were various ways the shops can (and did!) alter the operation of the systems, I hope others in the community will join in with additions and corrections. Currently in Run8 The operation of the brake valves currently in Run8 are based on the Westinghouse 26-L system which was introduced in 1957. The automatic valve features (from left to right) Release, Minimum Reduction (that initial 6psi reduction), Service Zone (the further right you go, the more reduction you get), Suppression (recovery after a "penalty application"), Continuous Service (leave it long enough and pressure will go to 0), and Emergency. The independent brake has Release and an Application Zone, where locomotive brake cylinder pressure is proportional to the position of the brake valve handle. To "bail off" the locomotive brakes, the handle is depressed. The important thing to remember about 26-L and its successors it that they are all self-lapping. By that, I mean that as you move both the automatic and independent valves further into the Service Zone, pressure will reduce (or increase in the case of the independent) in relation to the movement of the handle. No. 6-ET The 6-ET was introduced in 1906 and became the standard brake system on steam locomotives for many years. The automatic positions were: Release (this opened the brake line directly to the main reservoir). Kind of a "cheat" (similar to F7) you had to be carefull not to overcharge the brake line beyond the current "normal" setting (similar to the 90 psi / 110 psi settings we use today). Release was followed by Running (kept the brake line fully charged based on the EQ reservoir), Holding (released the train brakes, but kept the engine/tender brakes set), Lap (more on that in a moment), Service, and Emergency. In order to make a brake pipe reduction the engineer would put the valve into Service and carefully watch the Equalizing Reservoir (EQ) pressure. When the EQ reduced to the proper level he would place the valve back into Lap. This is because unlike later systems, 6-ET was not self-lapping. Leave the system in Service long enough, and the brake line pressure would go to 0 psi. The independent valve had Release ("bail"), Running, Lap, Service, and Quick Service. To apply brakes on the engine and tender, the engineer would put the valve into Service. When the brake cyinders reached the desired pressure, the engineer would put the valve into Lap to hold that pressure. Quick Service was like service except it applied pressure more quickly. Please follow the following link to a .pdf download for a 14EL brake. The only difference between the 14EL and the 6-ET was the 14EL was made as a single casting compared to the two individual castings for the 6ET. 14 EL was designed for diesel-electric and electric locomotives and had additional features for multiple unit operation. http://www.hawaiianrailway.org/maintenance/14-ELBrakeEquipment.pdf No. 8-ET The 8-ET is the system that the Southern Pacific GS-4's were equipped with. Union Pacific's 800 Class 4-8-4s were also outshopped with this air brake schedule. In fact, the 4449 still operates with it's 8-ET system. In operation, there was only one difference between the 8-ET and 6-ET systems. The 8-ET replaced the "Hold" position with "First Service". Like the 26-L, Minimum Reduction applies an initial 6 psi reduction by connection the equalizing reservoir to a reduction limiting reservoir to give an initial 6-8 pound reduction, after which brake pipe pressure would continue to reduce at a slower than service rate. Beyond that, the system was still fully manual. The independent valve operated exactly as the 6-ET. And why does this matter? It matters that assuming the folks at Run8 follow usual practice of matching prototypes as much as possible, they are going to have to program a whole new brake system for the GS-4's. ''We're ''going to have to learn how to run a system that required much more control of the brake valves as well as closer attention to the pressure guages!